Piezoelectric bodies are now widely used as materials for functional electronic components such as actuators and sensors. As piezoelectric materials for use in these applications, perovskite-type ferroelectric materials are mainly used which are represented by the general formula Pb(Zr,Ti)O3 referred to as PZT. However, the PZT, which contains harmful Pb (lead), is thus an unfavorable material for protecting the natural environment.
Therefore, various non-lead piezoelectric materials have been now actively researched and developed. One of the non-lead piezoelectric materials is a perovskite-type ferroelectric material represented by the general formula (K,Na)NbO3, which is referred to as KNN. KNN (potassium sodium niobate) has been attracting massive attention because of having piezoelectric characteristics comparable to PZT.
For example, Patent Document 1 proposes a potassium sodium niobate thin film represented by (K1-xNax)NbO3 (0≦x≦1), which is created by a sputtering method. Further, Patent Document 1 discloses a high piezoelectric constant which can be achieved by creating a potassium sodium niobate (KNN) thin film with an average crystal grain size of from 0.1 μm to 1.0 μm and the crystal grains elongated in the substrate thickness direction.
In addition, Non-Patent Document 1 proposes a stoichiometric K0.5Na0.5NbO3 thin film and a thin film of the composition with K and Na each 10 mol % excessively added thereto, which are created by a chemical solution deposition (CSD) method. Further, Non-Patent Document 1 discloses improvements in leakage current characteristics, which are observed by 10 mol % excessively adding each of K and Na.    Patent Document 1: Japanese Patent Application Laid-Open No. 2008-159807    Non-Patent Document 1: Japanese Journal of Applied Physics, Vol. 49, 2010, 095805